
Probability and Statistics Basic Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
March 14th, 2015, 10:16 PM  #1 
Newbie Joined: Nov 2014 From: math Posts: 27 Thanks: 1  Confidence Interval  conceptual understanding
In a randomly selected sample of 500 registered voters in Kowloon, 200 individuals say that they plan to vote for Candidate A in the upcoming election.  If the survey were repeated a lot of times, we expect 90% of the confidence intervals constructed will contain the proportion of all Kowloon voters who plan to vote for Candidate A.  If the survey were repeated a lot of times, we expect 90% of the confidence intervals constructed will contain 40%, which is the estimate of the proportion of Kowloon voters who vote for Candidate A. I think the second statement is right, but I was wrong. Why? What's the difference between the two? 
March 15th, 2015, 01:49 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,785 Thanks: 707 
40% is an estimate of the proportion, but it is not necessarily the true proportion.

March 15th, 2015, 08:27 PM  #3 
Newbie Joined: Nov 2014 From: math Posts: 27 Thanks: 1 
Does that mean when we do the survey many times, it is expected that the intervals we get will be the true proportion?

March 16th, 2015, 03:52 PM  #4 
Global Moderator Joined: May 2007 Posts: 6,785 Thanks: 707 
One of the basic theorems in probability theory is the law of large numbers, which says (essentially) that a sample average converges to the mean as the sample size gets bigger.


Tags 
conceptual, confidence, interval, understanding 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Confidence Interval  Khorner  Advanced Statistics  1  August 4th, 2014 11:56 AM 
Confidence interval  GoldenMedal  Probability and Statistics  1  June 20th, 2014 05:48 PM 
Confidence interval  tay101  Advanced Statistics  1  January 7th, 2014 09:37 AM 
Confidence Interval please help  KatM  Advanced Statistics  0  May 12th, 2009 10:21 AM 
Confidence Interval  shalomhk  Advanced Statistics  1  August 1st, 2008 12:50 PM 